The present invention relates to an improvement in UOE pipe manufacturing apparatus and, more particularly, to an improved automatic tab plate welding apparatus for welding a tab plate (a small steel piece) to each of four corners of a plate of pipe material (hereinafter called a plate) before the forming of a pipe.
The UOE pipe manufacturing process is widely used in the manufacture of large-diameter welded pipes. In the UOE process, a plate which has been cut to predetermined size is planed on its edges, formed into a U-shaped form in section by a U-ing press, formed into an 0-shaped form in section by an O-ing press, welded along a seam to form a pipe, and expanded and shaped into a large-sized welded steel pipe by an expander inserted thereinto.
In welding along the seam of the pipe formed into the 0-shaped form in section, however, welding defects usually occur at the beginning and at the end of the welding seam. Therefore, tab plates are attached to the ends of the O-shaped pipe before welding so that these welding defects will be confined to the tab plates. However, the manual operation of attaching these tab plates is dangerous and requires fairly high skill.
Accordingly, a method of forming portions corresponding to these tab plates in the plate in advance was proposed in United Kingdom Pat. No. 1,439,787. Even though this method has made the tab plate attaching operation unnecessary, it has the disadvantage that yield is decreased due to the necessity to provide cuts or notches at the ends of the plate.
On the other hand, the present applicant disclosed a method of welding a tab plate to each of four corners of a plate before the pressing step and thereafter performing pressing and welding steps (Japanese Patent Publication No. 18158/84 Official Gazette). Next, the applicant disclosed an invention entitled "Automatic Tab Plate Welding Apparatus" (Japanese Patent Public Disclosure No. 17362/86 Official Gazette) for carrying out the previously disclosed method.
Said automatic tab plate welding apparatus has, as shown in FIGS. 20 and 21, four welding devices 1 which are disposed in twos on both sides of a pass line of a plate A and which are adapted to approach the four corners of the plate A resting on the pass line from the sides and thereby to weld tab plates B to the corners. Each of the welding devices 1 runs with wheels 36 on parallel rails 35 laid at right angles to the direction of passage of the plate A shown by an arrow and approaches the plate A which has stopped and rests on the rails. A lower bedplate 32 having the wheels 36 is provided in the rear part thereof with a tab plate store box 7 for storing a plurality of tab plates B and a tab plate feeding device 8 for attracting one of the tab plates in the store box 7 and feeding it to a tab-plate positioning table 22 as will be described in detail hereinbelow.
The lower bedplate 32 is provided on the front part thereof with parallel rails 34 and an intermediate bedplate 31 slidable forward and backward along the rails 34 on the lower bedplate. The intermediate bedplate 31 is likewise provided thereon with parallel rails 33 and an upper bedplate 30 slidable sideways along the rails 33 on the intermediate bedplate 31, that is in the direction parallel to the side end face of the plate A.
The upper bedplate 30 is provided thereon with all the essential devices such as a welder 11 having a vertical pair of welding torches 12, mounts 13 therefor, and a wire feeding device 3, a clamping device 5 for holding the plate from above and below, the tab plate positioning table 22, and a tab plate setting device 6 for fixing the tab plate B on the tab plate positioning table 22.
The welding device 1 runs with the lower bedplate 32 to the neighborhood of the plate A and stops there. The intermediate bedplate 31 moves forward from there and stops at the position at which a holding plate 23 disposed on a side end face of the tab plate positioning table 22 abuts against a side end face of the plate A. Then, the upper bedplate 30 slides along the side end face of the plate A (obliquely toward the upper left corner of FIG. 20) and stops at the position at which a stopper 19 disposed on the forward end of the tab plate positioning table 22 abuts against the forward end of the plate A. In this manner, the tab plate positioning table 22 is properly positioned and the plate A is clamped by the clamping device 5. Then, the tab plate B which has been supplied and placed on said table 22 by the tab plate feeding device 8 is tightly urged and clamped to the holding plate 23 and the forward end of the plate A by the action of urging blocks 26 and 27 constituting the tab plate setting device 6, and, thereafter, welding is started.
Since the mounts 13 for the welding torches 12 are vertically and horizontally slidable along the side walls of the welder 11, the welding torches 12 can be adjusted in height and move parallel along the welding line to automatically weld the tab plates B to the corners of the plate A.
However, service experience and on-line tests have shown that the conventional automatic tab plate welding apparatus described above has certain problems as follows:
(i) Since the weight of the welding device 1 as a whole is too large, the lower, intermediate and upper bedplates 32, 31 and 30 cannot be moved smoothly.
(ii) While a vertical pair of welding torches 12 facing upward and downward, respectively, are used, the upward welding torch 12 is very unstable and ill-suited for a mass production line (when welded from above and below without providing adequate beveling, sufficient depth of penetration is not obtainable and, particularly in thick tab plates, sufficient coupling strength is not obtainable either).
(iii) The entire production line must be stopped each time the tab plates B are supplied to the tab plate store box 7 or the store box 7 is exchanged.
(iv) Since the amount of movement of the welding torches 12, that is the welding length, is fixed, only tab plates of this fixed width can be used with the welding apparatus.
Accordingly, an object of the present invention is to provide an automatic tab plate welding apparatus in which all of the problems of the conventional apparatus described above can be obviated.